Coated paperboard trays for serving food, particularly packaged convenience food, are becoming more and more popular. With the advent of the microwave oven, the trend in the industry toward paperboard trays has accelerated, since as is well known, aluminum containers cannot be effectively used in the microwave ovens. With the development of polyester coatings for the tray, the same tray can also be placed in a conventional radiant heat oven without adverse effects.
This food serving tray has not only become very popular for home use, but also where large volumes of food must be cooked and used within a short period of time, such as in the airline industry and in hospitals. The food prepared and placed in the coated paperboard trays can be frozen and then quickly reheated, generally in a microwave oven, for serving. Since the serving trays are disposable, the washing of dishes is eliminated.
In the field of packaging convenience foods, Kliklok Corporation, the assignee of the present invention, is the leader. This company is the assignee of the prior patent application entitled "Method and Apparatus for Forming a Flanged Tray," Baker et al., Ser. No. 55,050, filed July 6, 1979. In this application, a highly efficient tray forming method and machine is shown and claimed. In the application, a standard flanged ovenable tray is disclosed that is successful in this field.
The Kliklok prior art ovenable tray is coated with the polyester resin film. The tray is extremely strong including reinforced corners in order to prevent collapse of the tray when filled and during stacking and handling. The flange around the top of the tray also reinforces the tray, and in addition provides a convenient way of applying a simple lid to the tray. The lid is particularly useful in instances where foods are to be cooked while sealed in order to retain moisture and the flavor of the food.
While the tray of the prior art has thus been successful, and is capable of storing many different kinds of food, there has been identified a need for a tray with reinforced corners that is leakproof substantialy to the very top of the tray. In the past, when forming the reinforced corner on a high-speed packaging machine such as shown in the prior Baker et al. application '050, the leakproof characteristic could be extended only up a portion of the side of the tray. It can be seen that while this prior art arrangement was suitable for some products, such as bakery products where no liquid is involved in the packing, such trays were not suitable for liquid or semi-liquid products, which represent a large proportion of the packaged foods.
Accordingly, it is an object of the present invention to provide an improved tray having reinforced corners which are leakproof, and which tray can be formed on high-speed machinery.
It is another object of the present invention to provide a tray formed of ovenable paperboard suitable for use in conventional and microwave ovens having reinforced corners and a reinforcing flange around the top of the tray.
It is still another object of the present invention to provide a gusset corner for a tray wherein the corner may be easily formed on existing machines and provides reinforcement and full-depth leakproofness to the tray.
It is still another object of the present invention to provide a flanged, ovenable tray and gusset corner therefor wherein the gusset structure is firmly and securely held against the adjacent side wall of the tray for reinforcement of the corner and for sealing along the full depth of the side wall.